When you are stopped for suspicion of DUI or some other traffic violation, the officer is entitled to detain you if the officer reasonably suspects that you were driving under the influence of alcohol or drugs. That suspicion is usually formed as soon as the officer smells an alcoholic beverage on your breath. The detention gives the officer a chance to investigate that suspicion.
Police officers are trained to investigate suspected cases of DUI in a variety of ways. One of the most common is to administer field sobriety tests (FSTs). They come in two flavors: nonstandard FSTs and the more common standardized FSTs.
Before the National Highway Traffic Safety Administration (NHTSA) gave its blessing to “standardized” FSTs, police departments and individual officers invented their own tests. “Close your eyes and touch your nose” was a common test despite the absence of any scientific evidence that sober people touch their noses more often than people who are under the influence of alcohol.
Other tests, including “recite the alphabet backward,” were nearly impossible for anyone to perform. That allowed police officers to make lots of arrests, but it also resulted in careful judges throwing out the evidence that resulted from those arrests.
To be used against a DUI defendant at trial, the evidence must be obtained legally. Evidence is legally acquired after an arrest only if the arrest is legal. Basing an arrest on less than probable cause is not legal. Since the most compelling evidence of DUI (including blood and breath test results) usually follows an arrest, DUI cases are typically dismissed when the evidence obtained after an illegal arrest is thrown out.
Because the use of nonstandard FSTs resulted in the dismissal of many DUI prosecutions, NHTSA set about developing standardized FSTs that could reliably predict whether a driver was under the influence of alcohol. NHTSA created and “validated” three standardized FSTs. The “validation” resulted from junk science — officers who were trained to perform the tests administered them to officers who volunteered as test subjects and the results were evaluated by other officers — but they have become the gold standard for establishing probable cause to arrest suspected drivers.
There are three standardized FSTs. The first is the horizontal gaze nystagmus (HGN) test. Nystagmus is a twitching or jittery movement that is present in everyone’s eyes when they look to the left or right without moving their heads. According to NHTSA, most people will exhibit no nystagmus while looking straight ahead while everyone will exhibit nystagmus when they move their eyes all the way to the left or right.
The HGN test is based on the theory that people who are under the influence of alcohol exhibit nystagmus sooner than people who are not under the influence as they move their eyes to the side. If the onset of nystagmus occurs before the eyes reach a 45-degree angle, NHTSA believes that the person probably has a blood alcohol concentration of at least 0.08.
Officers are trained to tell a driver to look straight ahead and to follow a moving object (like a pen or a finger) with their eyes. The officers look for how well the eyes track the object and for how “smoothly” the eyes move, but the key to the test is whether the officer observes nystagmus before the eyes reach a 45-degree angle.
The other two tests are “divided attention” tests. They test for balance on the theory that people who are under the influence lose their balance more quickly than sober people. They also test how well the driver remembers and follows instructions. Officers are instructed to assess a point for each specific way in which a test subject fails to perform the test as instructed. They are also taught that a certain number of points should be regarded as evidence of DUI.
The walk-and-turn test requires a driver to walk in a straight line (usually an “imaginary” line) by taking nine steps while walking heel-to-toe. The driver is told to turn by taking a series of short, choppy steps and to repeat the test by walking nine steps in the other direction. The driver is also told not to raise his or her arms during the test. Raising the arms, taking the wrong number of steps, deviating from a straight line, leaving more than a half-inch gap between heel and toe, and turning with a pivot instead of choppy steps will each result in the assessment of a point.
The one-leg stand requires a driver to stand with one foot raised six inches from the ground, to keep the foot elevated until the officer tells the driver to stop (30 seconds unless the officer cheats), and to keep his or her arms at the side of the body. Raising the arms, hopping, putting the foot down too soon, not lifting the foot high enough, and sticking the leg out instead of lifting the foot will all result in the assessment of points. Falling over while engaging in either the one-leg stand or the walk-and-turn will usually result in an immediate arrest.
DUI defense attorneys challenge FST results at two stages. First, during a suppression hearing to contest the officer’s claim that the arrest was justified by probable cause. Second, during a trial.
Judges tend to be jaded after hearing so many officers testify about FSTs, but it is all new to most jurors. Armed with the NHTSA training manual, a defense attorney can establish through cross-examination that the officer remembers little of his or her FST training. Officers almost never remember how to administer the HGN test correctly. Based on the training manual, the officer will need to admit that if the test was not administered according to NHTSA’s precise instructions, the results are not valid.
DUI defense attorneys score major points with juries by establishing that the officer made mistakes while administering the FSTs. Videos were taken by squad car cameras often confirm those mistakes while establishing that the test performance was better than the officer claims. Skilled cross-examination about FSTs often results in the tests helping the defense more than the prosecution.